1. Technical Field
The present disclosure relates to reconfigurable PLLs within local oscillators, where the local oscillators are usable in multi-standard transceivers.
2. Background Information
In the early days of cellular telephone technology, a given cellular telephone generally communicated using only one cellular telephone standard. For example, there were cellular telephones that used the GSM (Global System for Mobile Communications) standard and there were cellular telephones that used the CDMA (Code Division Multiple Access) standard. Over time cellular telephone technology evolved. The corresponding standards evolved as well. Cellular telephones became more complex and came to have more and more functionality and processing power. A cellular telephone handset nowadays may include circuitry for communicating using many different wireless communication technologies of different types. Recently cellular telephones have been introduced that can use multiple different completing cellular telephone technologies. Such a cellular telephone may, for example, be able to engage in a cellular telephone communication using the GSM standard in one environment, and then may be able to reconfigure itself so that it can then engage in a cellular telephone communication using another standard such as CDMA1× or WCDMA in another environment. One way to provide such multi-standard functionality was to package one radio for communicating using one standard along with another radio for communicating using another standard. Each of the two radios had its own local oscillator that had particular performance characteristics suitable for the standard used by the radio. Another way to provide such multi-standard functionality is for both of the radios to share certain portions of their circuitry. For example rather than providing one local oscillator for use with one standard and other local oscillator for use with another circuit, versatile Digitally Controlled Oscillator (DCO)-based local oscillators have come to be used. In such a multi-standard system, a single DCO-based local oscillator might be configured in a first way to support communications using one standard and might be configured in a second way to support communication using a second standard. Although DCO-based multi-standard designs work adequately well in may applications, further improvements in the design of multi-standard cellular telephones are desired.